sour mulch - help!

Asked May 20, 2019, 11:08 PM EDT

Hi there - Last year our landscaper installed mulch after we had planted annuals all over the yard, and it turned out he put in sour mulch and it burned and outright killed hundreds of dollars worth of plants. We told him this year to be sure the mulch was good and he promised to do so. Out of an abundance of apparently much needed caution we waited this year to plant our annuals until after they had installed the mulch and we are beside ourselves that once again they have installed mulch that is completely sour and stinks like crazy. As before, we have purchased hundreds of dollars of annuals and we are glad we waited to plant. Our question is, now that the sour mulch is installed in the beds, how long do we need to wait before it is safe to plant? We don't want to waste our time and money again planting annuals only to have the mulch burn/kill them. Is there anything we can do to speed this along? What do you recommend we do now? Other than fire our landscaper... Thank you for your help!

Maryland mulch abiotic issues flowers: annuals and herbaceous perennials

2 Responses

Hi- it's hard to say how long it will take for the mulch to naturally "de-toxify." The safest thing would be to have the landscaper remove the mulch to an unused area of your yard where it can "air out" in a windrow not more than 2 ft. high. The mulch could be used once the smells have fully dissipated. Meanwhile you could plant and use fresh, high quality mulch.

You could also try to spread it out a bit where it now lays in the beds to get more air into it. Sunny, breezy weather and adequate soil moisture will help reduce the wood alcohols and shorten the time it will take for the mulch revert to an aerobic state. Once the smell is gone you can plant a few test annuals to see how they respond.

Sorry, forgot to mention that you may be able to leach a good bit of the wood alcohols with water. Try soaking the mulch really well in the morning and letting it dry for a few days. That might do it.

Our mulch fact sheet has some information on sour mulch:
https://extension.umd.edu/sites/extension.umd.edu/files/_docs/programs/hgic/HGIC_Pubs/TreesandShrubs...